Is that not pretty much what Rust's procedural macros are? [0]
Except for the fact that they do not allow emitting invalid token streams (which is something you don't want anyways), it can do any arbitrary manipulation of source code, but in a way that is integrated with the compiler and less prone to breaking the program.
[0] https://doc.rust-lang.org/reference/procedural-macros.html
cpp_call! { fn foo() { ... } }
#[cpp_call] fn foo() { ... }
Textual substitution is less rigorous. It tells the compiler to replace a string with another, wherever it is seen. There's no restriction that it must be valid token input to be replaced or that it needs to be an explicit usage of the macro.
Reminds me of some of stringification abused in the Linux kernel. What looks like a function call passing the literal text param1## as an argument, where it would then trigger a different stringification in a subsequent preprocessor pass that prepended ##foo to the passed argument.